Trying again, there's one point: What really made Figma successful is design moving from being made in "professional software" (like say Photoshop, Premiere, Visual Studio, Maya) to "collaboration software" (like Slack, Google Sheets), and that this was made possible because "flat design" is less technically demanding than the "skeumorphic" design it replaced.
(Sorry I wasn't clearer, I struggle on how to make points like this succinctly without is sounding a bit disjointed.)
I agree with one of your points (that where Figma really succeeded is that it understood better than anyone else the collaborative nature of web design), but I disagree that flat design vs. skeuomorphic makes much of a difference. I've seen more "realistic" designs where the actual iconography/images are created in something like Photoshop and then just imported to Figma, and Figma handles it fine.
Point being that I think that even if all apps still had the design aesthetic of 2008 iPhone apps that Figma still would have succeeded.
(Sorry I wasn't clearer, I struggle on how to make points like this succinctly without is sounding a bit disjointed.)